[Bug optimization/14903] New: tail call optimization does not work with char return type

[Bug optimization/14903] New: tail call optimization does not work with char return type

[cesarb at nitnet dot com dot br]

(old bug but couldn't find on bugzilla, see
http://gcc.gnu.org/ml/gcc/2002-09/msg00632.html )

When compiling:
extern unsigned char f(void);
unsigned char g(void) { return f(); }

With:
gcc -W -Wall -Os -fomit-frame-pointer -save-temps -c

The result is:
g:
        call    f
        movzbl  %al, %eax
        ret

Notice the superfluous zero extension (signed char has a sign extension
instead). Without it, the call would be optimized to a jmp.

This makes it harder to try to use tail-recursive functions as if they were
loops (where the loop goes through 3-4 functions with one or two of them looked
up on a table).

Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.3/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib
--enable-nls --without-included-gettext --enable-__cxa_atexit
--enable-clocale=gnu --enable-debug --enable-java-gc=boehm
--enable-java-awt=xlib --enable-objc-gc i486-linux
Thread model: posix
gcc version 3.3.3 (Debian 20040401)

-- 
           Summary: tail call optimization does not work with char return
                    type
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: cesarb at nitnet dot com dot br
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14903

[Bug optimization/14903] tail call optimization does not work with char/short return type

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-10 02:42 -------
Confirmed, related to 14440, 14472, and 14441 but should depend only on PR 14441 as the problem 
is that the char is promoted to int.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |pessimizes-code
   Last reconfirmed|0000-00-00 00:00:00         |2004-04-10 02:42:38
               date|                            |
            Summary|tail call optimization does |tail call optimization does
                   |not work with char return   |not work with char/short
                   |type                        |return type


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14903

[Bug optimization/14903] tail call optimization does not work with char/short return type

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-09 22:30 -------
This is a dup of bug 14441, the patch which fixes that also fixes this one.

*** This bug has been marked as a duplicate of 14441 ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14903